In the UK, drivers are told to stay in the lane closest to the edge of
the road (lane 1), pull out to overtake, and pull back in afterwards.
In mainland Europe they actually do this.

The typical motorway offers only two lanes each way; major
non-motorway highways may be just a two-lane road to carry all
traffic. I do more overtaking onto the other side of the road in a
couple of weeks than in the entire rest of the year, when I'm mostly
driving on British motorways.

With vehicles travelling at a wide variety of speeds, the standard
approach is to stay in lane 1 until the last chance you'll get to
overtake the vehicle in front without braking. It's apparently
entirely acceptable to cause a vehicle coming up in lane 2 to have to
decelerate to avoid hitting you. The other side of that is that you
are expected to pull back quickly after completing the overtaking if
there's anything behind you.

Not everyone does pull back over, especially in Belgium; pulling a
little closer soon after they clear the vehicle they're overtaking as
if you were going to go ahead at your preferred speed, and perhaps
weaving back and forth a little to remind them of your presence,
usually works. Some people flash headlights, usually a long flash
rather than the peevish short flash that most British drivers seem to
favour. Everyone drives much closer to the vehicle in front than I
consider reasonable; judging by German-registered cars I've been in, I
think they mostly also have rather sharper brakes than is usual in the
UK.

Obviously it only works if the roads aren't completely packed; once
they fill up, e.g. near a major city, the frequent lane changes make
things harder work for everyone.

Some other notes:

On Belgian and Dutch motorways, toilets generally cost (€0.50); in
theory you get a voucher for the same value you can use in the shop,
but then you're buying something at motorway service area prices, and
nothing's less than €2 or so.

On the Autobahn there are various grades of rest area: basic ones
(Rästplatz) may or may not even have a toilet (look for the "WC" on
the sign), but are free; Räststatte usually have fuel and at least a
shop, perhaps a restaurant in the coffee-shop style; the Rästhof has
somewhere to sleep; and the Autohof is a truck stop where they will
charge you for the toilets.

Danish and Swedish roads have a similar Rästplatz-style system, but
the larger areas seem to be less formal; often you'll be directed off
the road to a local garage instead of having a dedicated service area.
In Finland, it's either roadside areas without facilities or garages;
there don't seem to be any small rest areas with toilets.